In recent years, there has been a problem of destruction of coral reefs such as bleaching of coral communities and extinction of coral due to the rising sea temperature and the like resulting from landfill and the global warming. Therefore, in recent years, attempts of recovering coral reefs by artificially cultivating coral have been proposed. Patent Literature 1 proposes an apparatus that cultivates coral by arranging a cathode to which coral is attached and an anode in sea water and applying an electric current between the cathode and the anode.